i. Prosthetic Vascular Grafts Including Venous Valvular Implants
Modern vascular surgical procedures often involve the grafting of a tubular prosthetic implant of artificial or natural origin into an existing blood vessel for the purpose of replacing or bypassing a segment of diseased or damaged blood vessel. Many such procedures are accomplished by surgically removing the diseased or damaged segment of blood vessel, and subsequently replacing the removed segment of vessel with an appropriately sized tubular implant graft. The implant graft is typically held in place by anastomosing the ends of the implant graft to the opposing ends of the resected blood vessel.
In individuals who suffer from chronic venous valvular insufficiency, vascular grafting procedure have utilized to transplant functioning venous valves into the affected veins of the lower extremities. The transplantation of functioning venous valves in such individuals is therapeutically important as chronic incompetence or absence of venous valves into the veins of the lower extremities is known to give rise to numerous pathological consequences. For example, incompetence or absence of venous valves at the saphenofemoral or saphenopopliteal junctions may result in noncosmetic varices of the primary and/or secondary veins of the lower leg and ankle. Additionally, deep venous hypertension of the lower limb may occur. Such venous hypertension may result in lymphedema, aberrant pigmentation of the skin and, in severe cases, the formation of necrotizing lesions known as "venous ulcers".
Surgical transplantation of one or more functioning venous valves into a valve-deficient vein is a viable means of restoring venous valvular function to the valve deficient vein. The routine use of venous valve "transplant" procedures has heretofore been largely limited to autograft procedures. Such autograft procedures require the initial surgical excision of an autologous segment of viable vein (i.e. vein having a functioning venous valve therein) from one site within the patient's body, followed by subsequent transplantation of the harvested autograft to other veins wherein the venous valvular insufficiency has occurred. Such autograft transplant procedures are problematic because of (a) difficulties encountered in locating suitable segments of vein having viable venous valves therein and/or (b) the necessity of forming a separate incision or second surgery to harvest the venous valve autograft and/or (c) size mismatching of the harvested venous valve autograft relative to the implant site as may result in subsequent thromboembolic complications and failure of the implanted valve.
In view of the limitations and shortcomings of autograft venous valve transplantation procedures, it is desirable to develop artificial and/or preserved venous valve implants from cadaverous human or animal sources for subsequent transplantation into a human patient. The availability of artificial or bioprosthetic venous valve implants would eliminate the need for second-incision harvesting of homograft tissue and would enable the surgeon to select from an available range of graft sizes to obtain a graft which is specifically size-matched to the diameter of the resected blood vessel.